Re: [PATCH 4/7] block: Introduce a new ioctl for simple copy

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Aug 17, 2021 at 03:44:20PM +0530, SelvaKumar S wrote:
> From: Nitesh Shetty <nj.shetty@samsung.com>
> 
> Add new BLKCOPY ioctl that offloads copying of one or more sources ranges
> to a destination in the device. COPY ioctl accepts a 'copy_range'
> structure that contains destination (in sectors), no of sources and
> pointer to the array of source ranges. Each source range is represented by
> 'range_entry' that contains start and length of source ranges (in sectors)
> 
> MAX_COPY_NR_RANGE, limits the number of entries for the IOCTL and
> MAX_COPY_TOTAL_LENGTH limits the total copy length, IOCTL can handle.
> 
> Example code, to issue BLKCOPY:
> /* Sample example to copy three source-ranges [0, 8] [16, 8] [32,8] to
>  * [64,24], on the same device */
> 
> int main(void)
> {
> 	int ret, fd;
> 	struct range_entry source_range[] = {{.src = 0, .len = 8},
> 		{.src = 16, .len = 8}, {.src = 32, .len = 8},};
> 	struct copy_range cr;
> 
> 	cr.dest = 64;
> 	cr.nr_range = 3;
> 	cr.range_list = (__u64)&source_range;
> 
> 	fd = open("/dev/nvme0n1", O_RDWR);
> 	if (fd < 0) return 1;
> 
> 	ret = ioctl(fd, BLKCOPY, &cr);
> 	if (ret < 0) printf("copy failure\n");
> 
> 	close(fd);
> 
> 	return ret;
> }
> 
> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
> Signed-off-by: SelvaKumar S <selvakuma.s1@samsung.com>
> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
> ---
>  block/ioctl.c           | 33 +++++++++++++++++++++++++++++++++
>  include/uapi/linux/fs.h |  8 ++++++++
>  2 files changed, 41 insertions(+)
> 
> diff --git a/block/ioctl.c b/block/ioctl.c
> index eb0491e90b9a..2af56d01e9fe 100644
> --- a/block/ioctl.c
> +++ b/block/ioctl.c
> @@ -143,6 +143,37 @@ static int blk_ioctl_discard(struct block_device *bdev, fmode_t mode,
>  				    GFP_KERNEL, flags);
>  }
>  
> +static int blk_ioctl_copy(struct block_device *bdev, fmode_t mode,
> +		unsigned long arg)
> +{
> +	struct copy_range crange;
> +	struct range_entry *rlist;
> +	int ret;
> +
> +	if (!(mode & FMODE_WRITE))
> +		return -EBADF;
> +
> +	if (copy_from_user(&crange, (void __user *)arg, sizeof(crange)))
> +		return -EFAULT;
> +
> +	rlist = kmalloc_array(crange.nr_range, sizeof(*rlist),
> +			GFP_KERNEL);
> +	if (!rlist)
> +		return -ENOMEM;
> +
> +	if (copy_from_user(rlist, (void __user *)crange.range_list,
> +				sizeof(*rlist) * crange.nr_range)) {
> +		ret = -EFAULT;
> +		goto out;
> +	}
> +
> +	ret = blkdev_issue_copy(bdev, crange.nr_range, rlist, bdev, crange.dest,
> +			GFP_KERNEL, 0);
> +out:
> +	kfree(rlist);
> +	return ret;
> +}
> +
>  static int blk_ioctl_zeroout(struct block_device *bdev, fmode_t mode,
>  		unsigned long arg)
>  {
> @@ -468,6 +499,8 @@ static int blkdev_common_ioctl(struct block_device *bdev, fmode_t mode,
>  	case BLKSECDISCARD:
>  		return blk_ioctl_discard(bdev, mode, arg,
>  				BLKDEV_DISCARD_SECURE);
> +	case BLKCOPY:
> +		return blk_ioctl_copy(bdev, mode, arg);
>  	case BLKZEROOUT:
>  		return blk_ioctl_zeroout(bdev, mode, arg);
>  	case BLKGETDISKSEQ:
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 7a97b588d892..4183688ff398 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -76,6 +76,13 @@ struct range_entry {
>  	__u64 len;
>  };
>  
> +struct copy_range {
> +	__u64 dest;
> +	__u64 nr_range;

If the maximum number of elements in the range list is 1<<12, there's no
need for this to be larger than a u16, right?

> +	__u64 range_list;

Pointers embedded in a structure are /not/ a good idea, because this
will create a lot of compatibility headaches for 32-bit binaries running
on 64-bit kernels.  Please just make the size of this header structure
a multiple of 8 bytes and put the range_entry list immediately after it.

struct copy_range {
	__s64 dest_offset;
	__u32 nr_range_entries;
	__u32 flags;
	__u64 reserved[2];
};

struct __user range_entry *re = ((struct range_entry *)(copyhead + 1));

copy_from_user(&urk, re...);

--D

> +	__u64 rsvd;
> +};
> +
>  /* extent-same (dedupe) ioctls; these MUST match the btrfs ioctl definitions */
>  #define FILE_DEDUPE_RANGE_SAME		0
>  #define FILE_DEDUPE_RANGE_DIFFERS	1
> @@ -197,6 +204,7 @@ struct fsxattr {
>  #define BLKROTATIONAL _IO(0x12,126)
>  #define BLKZEROOUT _IO(0x12,127)
>  #define BLKGETDISKSEQ _IOR(0x12,128,__u64)
> +#define BLKCOPY _IOWR(0x12, 129, struct copy_range)
>  /*
>   * A jump here: 130-136 are reserved for zoned block devices
>   * (see uapi/linux/blkzoned.h)
> -- 
> 2.25.1
>